LEDs generally emit in a Lambertian (hemispherical) pattern. It is conventional to mount one or more LEDs on a flat substrate, having a metal pattern, and provide a hemispherical lens (primary optics) over the LEDs to increase light extraction. The flat substrate and the LED construction inherently block sideways downward light, so the widest emission profile is Lambertian with a 180 degree maximum emission profile. To achieve other than a Lambertian profile from a lamp, secondary optics, including reflectors are used. Such reflectors add size and cost.
In some applications, it would be desirable to provide a compact lamp that has an emission profile wider than a Lambertian profile.